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    <script>
// 10. 检测是否是2到4位汉字
        function mark(str) {
            let re = /^[\u4e00-\u9fa5]{2,4}$/
            switch(re.test(str)) {
                case true:
                    console.log(str + "是一个2到4位的汉字")
                break;
                case false:
                    console.log(str + "不是一个2到4位的汉字")
                break;
            }
        }
        mark("水果案例");
    </script>
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